Today, Exelon announced it will buy Constellation Energy to form a utility that will span 38 states, parts of Canada and the District of Columbia.

The deal, once completed, will give Exelon a market cap of $34 billion and an enterprise value of $52 billion, plus a client base that includes 35,000 commercial and industrial customers and millions of households. The combined entity will sport 34 gigawatts of power-generating capacity and the country's largest nuclear fleet, with 19 gigawatts of generating capacity. The overall power mix will be somewhat clean, the company claims, with 55 percent of its capacity tied up in nuclear, 24 percent coming from natural gas and 8 percent coming from hydroelectric dams and renewables. (Constellation also bought CPower in September to expand its footprint into demand response services.)

Overall, the combined company will generate 226 terawatt-hours of energy a year.

It will also be the number-two distributor of gas and electricity in the country, serving 6.6 million customers in Pennsylvania, Maryland and Illinois.

Will it be an easy merger? No deal this size will ever go completely smoothly. The reliance on nuclear also poses a problem. Even before the Fukushima disaster, Constellation decided to put the Calvert Cliffs 3 plant in Maryland on hold because of the costs associated with getting a federal loan guarantee. Piling safety concerns on top of the financial issues is simply going to make building new nuclear plants, and extending the licenses on old ones, more difficult. (The anticipated cost was $1.6 billion for Calvert Cliffs 3, or $6 a watt. That's more than natural gas, coal and even wind with storage.)